Plasmid maintenance in E. coli will be studied by determining the in vivo transcription pattern of plasmid DNA. Two types of plasmids will be studied, R factors which confer multiple antibiotic resistance on cells which harbour them, and bacteriophage Pl which exists as a plasmid in lysogenic cells. Transcription of the plasmid DNA will be analyzed by DNA-RNA hybridization. Restriction nucleases will be used to prepare a physical map of these plasmids, and the transcription of individual fragments will be determined by DNA-RNA hybridization. Mutants which effect the level of conjugal transfer or antibiotic resistance will also be studied to determine the role of transcriptional control in the maintenance and transfer of R plasmids. Mutants which effect plasmid maintenance will be isolated and characterized, biochemically and genetically, to determine the nature and extent of the chromosomal genes involved in plasmid maintenance. BIBLIOGRAPHIC REFERENCES: Yun, T. and D. Vapnek (1977). Electron microscopic analysis of bacteriophage Pl, PlCm and P7; Determination of genome sizes, sequence homology, and location of antibotic resistance determinants. Virology 77:376-385. Alton, N. K. and D. Vapnek (1977). Transcription in E. coli of R plasmids repressed and derepressed for conjugal transfer. In "Microbiology 1977", D. Schlessinger, ed. American Society for Microbiology.